Very good thread! karachi mein kuch bhi ghoomne laiq nahi???
ghar ki murgi daal barabar...this may not be the perfect example but I think it serves the purpose. For Karachiites, its home and for some odd reason there are many places still undiscovered, atleast for me. Why, maybe because I take it for granted that I live in Karachi and will eventually see the undiscovered places sooner or later. But frankly, we really dont at least I havnt made an effort.
In my humble opinion, some of the places to see are...Flag Staff House, Mohatta Palace, Frere Hall, Bagh Ibn-e- Qasim (and the old temple inside), Wazir Mansion, Khaliq Dina Hall, PAF & Naval Museum, Old Clifton, The Gyeser/fountain, Hindu Gymkhana, National Museum, Quaid's Mazar etc etc....many , many more do exist which I may not be aware of. Also, there are many places of interest for foodies which I'm sure my fellow PWs will enlighten us on 
Thank you for starting this thread on Karachi. For one, Insha Allah I will try and add to this thread as and when possible.